People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Toxic Metals: Lead Exposure Can Incite Schizophrenia

May 31, 2013 03:31 PM By Anoopa Singh

In a mouse study, those predisposed to develop schizophrenia developed it faster when exposed to lead. Schizophrenia | Yuri Arcurs/Sh

For a long time, lead has been suspected of stunting growth and causing autism, but now the metal has been proven to trigger schizophrenia in those with a genetic predisposition toward the mental disorder.

Schizophrenia is a mental disorder that may develop slowly as a result of genetic predisposition or environmental factors. Genetic disposition comes in the form of a mutation in receptors that normally respond to neurotransmitters in the brain that create excitatory responses. Common symptoms are anxiety, difficulty concentrating, bizarre or erratic behavior caused by hallucinations, and a constantly racing mind. Physically, schizophrenia can cause a swelling of the brain because neurotransmitters are not completely utilized.

In 2004 and 2009 studies, scientists at Columbia University's Mailman School of Public Health suggested a connection between prenatal lead exposure and the development of schizophrenia later in life. The question of how exactly lead could do such a thing to one's brain remained until this current study was performed.

The researchers have found that mice with a genetic predisposition toward schizophrenia have reduced receptor sensitivity in the brain. The lack of receptor response to neurotransmitters creates the symptoms of schizophrenia. In mice with the predisposition, consumption of small amounts of lead caused anxiety, hyperactivity, and the enlargement of certain parts of the brain, such as the lateral ventricles, most affected by schizophrenia. These results are the same as what is seen in human subjects diagnosed with schizophrenia.

Before this study, the underutilization of brain receptors has been a key factor in the development of schizophrenia. The researchers in this study have found that lead acts to antagonize these receptors further, encouraging the formation of schizophrenia. In other mice tested, without a genetic predisposition toward schizophrenia, lead exposure did not cause the swelling of the brain or anxiety, but it did increase their involuntary movements and inability to calm down after being startled, which can be noted as the beginning stages of schizophrenia.

Future research may reveal to what extent schizophrenia is determined by environmental or genetic factors and their potential interactions. Researchers intend to look at whether lead can diminish certain types of neurons, known to be affected in schizophrenia patients, aside from the neurological activity changes, already proven in this study to be altered in schizophrenia and by lead.

Scientists are also interested in establishing the critical window for exposure that causes the most harm. This study focused on past natal exposure, but there may be more to find out about prental or in-utero exposure.

This study has implicated that exposure to dangerous environmental toxins, like lead found in household products including paint, electronics, and batteries, can severely alter mental health at any stage of human development.